Theory:

     Jaya and Velu walked along the roads for half an hour, until they came to a bridge across a dirty trickle of water. “We are in Triplicane now. See, that’s Buckingham Canal,” said Jaya.
 
     Velu stared. This was a canal? Near some puddles of water was a row of the strangest huts he had ever seen. They were built out of all sorts of things — metal sheets, tyres, bricks, wood and plastic. They stood crookedly and looked as if they would fall any moment.
 
     “Is this where you live? These houses are strange!” said Velu. “In our village, the houses are made of mud and palm leaves.”
Explanation:
 
Jaya and Velu took almost half an hour to walk along the roadside. After that, Velu and Jaya came near a bridgeDirty, polluted water was flowing nearby the bridge. On seeing the place, Jaya informed Velu that they are in a place called Triplicane.

Triplicane is one of the most crowded areas in Chennai city. There was a canal running through Triplicane, which is named as Buckingham Canal. Buckingham canal was a long freshwater canal constructed during British rule and was an essential waterway during the late nineteenth and early twentieth centuries. The canal connects most of the natural backwaters along the coast to Chennai (Madras) port. During the mid of twentieth century, after the effect of the tsunami, the water got polluted. Later on, no preventive measures were taken by the government to clean the canal. Currently, Buckingham Canal is the most polluted water system, in India and it gets polluted due to the mixing of contaminated water, industrial waste and sewage water into the canal.

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Wastewater from industries

Velu was staring at the canal after seeing the polluted water flowing through the canal. Nearby the canal, Velu saw a few huts. He had never seen such huts in his lifetime. The sheds were made of metal sheets, tyres, bricks, wood and plastic. The houses nearby the canal seemed to be very light, and they looked as if they would fall at any time.

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A hut made of metal sheets
 
The houses looked very strange, and after seeing the places, Velu asked Jaya whether she was living here. The homes in Velu's village were made up of mud and palm leaves. His village houses looked very beautiful and built in a good way using stones, bricks, wood, and palm leaves. It would not fall easily.
 
Meanings of the difficult words:
 
S.No
Words
Meanings
1
Puddles A small pool of liquid, especially of rainwater on the ground
2
BricksA small rectangular block typically made of fired or sun-dried clay, used in building
3
TsunamiA long, high sea wave caused by an earthquake or other disturbance
4
Palm leavesA type of thick leaves grow in Palm tree which is used for making huts in villages
5
Contaminated waterPolluted water
Reference:
National Council of Educational Research and Training (2008). It so happened. Children at work- Gita Wolf, Anushka Ravishankar and Orijit Sen (pp. 7-16). Published at the Publication Division by the Secretary, National Council of Educational Research and Training, Sri Aurobindo Marg, New Delhi.